Last fall, right before the temperature began to plummet to the mid 60s marking the beginning of a true Southern California winter, we witnessed a flurry of activity in the Nature Garden revolving around the blooming of the female Baccharis “coyote” bush. Several of the museum staff members rushed outside to witness the impressive array of beetles, bees, wasps, and flies feeding enthusiastically at the Baccharis banquet, and while most of us stood in awe of the sheer number of insects we saw crawling, hovering, and buzzing around, Brian advantageously captured images of several of the visitors.
One of my favorites of his spectacular photos is of the so-called “thick-headed fly” in the family Conopidae, a very unusual creature that has only shown up twice in our Malaise trap samples from our inventory of the North Campus. The two specimens we have collected so far represent two different genera, Physocephala and Zodion, which can be distinguished by the absence of simple eyes called ocelli (Physocephala) as well as differences in the wing venation and shape of antennae , but who both share the most distinguishing and jaw-dropping feature of some members of this family.
Take a close look at the abdomen (the last section of the insect body) and you will notice the swollen, pad-like structure and a distinctly curved tip near the end of the fly’s body. This modification of the abdomen is called the theca and it allows the female flies to accomplish the very difficult task of laying an egg into the body of other insects, specifically bees and wasps. The female fly, which superficially resembles a bee or wasp with its constricted abdominal “waist”, can be found sitting on flowers where it feeds on nectar and waits for the opportunity to spot a suitable host (which is quite possibly what the conopid in Brian’s photo was doing). The theca functions like a can opener with which she can grasp and pry open the abdominal segments of the host insect to enable her to inject an egg. Amazingly, conopid flies can accomplish this mid-air by dive bombing the bee or wasp and quickly clutching, prying, and injecting all while in flight! Conopids in general are relatively rare and most have only one generation per year, so we are thrilled to find that these incredible flies are perching and searching in our Nature Garden.